The present invention relates to a flow coat head for use on curtain-type coating machines, which are coming into extensive use in connection with the painting or coating of sheet stock, as for example, wall panel sheets and the like, in which a reservoir of the coating liquid is disposed above a conveyor structure adapted to carry the panels to be coated below and past the reservoir. The reservoir is provided with a suitable elongated discharge opening or slot extending entirely across the width of the panel to be coated and adapted to discharge the coating liquid in a vertical sheet or curtain-like formation, with the width of the discharge opening or slot being so dimensioned that a desired amount of coating liquid is deposited over the area of the receiving panel. By careful control of the amount of liquid discharged and the rate of travel of the receiving panel through the machine, the thickness of the deposited coating material may be quite accurately controlled, and a very uniform coating thickness can be achieved without ripples or waves to produce a very smooth finished surface.
The present types of machines of this type, while varying in details of construction, employ head structures utilizing the same basic concept with respect to the structure forming the discharge slot and the means for varying the effective width thereof to control the amount of liquid deposited upon the panel. Generally, such head structures involve the use of at least one movable blade or leaf member having an edge which defines one edge of the discharge slot, so that by lateral adjustment of such leaf the effective width of the discharge slot may be varied. It is common practice to employ a head structure comprising a fixed or rigid body having a discharge slot in its lower wall, usually of a size greater in width than the ultimate discharge slot to be employed, with the effective size of the discharge slot being controlled by a pair of leaf members carried by the head, at least one of such leaves being adjustable relative to the other for achieving the desired adjustment of the slot width. Such adjustment may be effected by a wide variety of means, as for example, cams, eccentrics, screw adjustments, etc.
A typical machine of this type is illustrated in U.S. Pat. No. 3,074,374, granted on Jan. 22, 1963 to R. Burkle, which illustrates adjustment of the slot by eccentric means.
It will be appreciated that the use of a rigid container structure having a relatively large opening or slot in the bottom wall thereof, the effective size of which is to be controlled by one or more laterally adjustable plates or leaves, presents a number of problems in connection with the use of the machine. It will be apparent that generally it is desirable to eliminate all moving parts operating in or in contact with the coating material, both from the standpoint of operation as well as cleaning. Constructions of this type normally employ a top cover to provide access to the interior of the head, which necessitates working from the top and thus awkwardly above the device during cleaning and other operations. One solution employed to eliminate this disadvantage has been to construct the head so that it may be swivelled to one side enabling the operator to work at the side of the machine, while another solution is to so construct the conveyor structures that they may be rectilinearly moved from an operative position adjacent the head to a work position spaced therefrom, thereby enabling relatively free access to the head structure.
It will also be appreciated that where moving parts are involved, the production cost is correspondingly increased and as the parts are in the flow of the coating liquid, accurate mating of the parts is normally necessary and in most cases provision must be made for effecting a separation of the parts to insure proper cleaning thereof.